package Text5;

import java.util.*;

public class Main {
    public static final int N = 110;
    static char[] s1 = new char[N];
    static char[] s2 = new char[N];

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        //我们用 * 表示正面，用 o 表示反面（是小写字母，不是零）。
        s1 = scanner.next().toCharArray();
        s2 = scanner.next().toCharArray();
        int len = s1.length;
        int res = 0;
        for (int i = 0; i < len; i++) {
            if (s1[i] != s2[i]) {
                res++;
                turn(s1, i);
                turn(s1, i + 1);
            }
        }
        System.out.println(res);
    }

    private static void turn(char[] s1, int x) {
        if (s1[x] == '*') {
            s1[x] = 'o';
        } else {
            s1[x] = '*';
        }
    }
}
